Only a fraction of the respondents (9%) said they were "very concerned" about third parties getting access to that information.

According to the survey, 91% said they had posted a photo of themselves online, compared to 79% in 2006, the last time the survey was conducted; 53% post e-mail addresses, compared to 29% in 2006; and 20% post their cell phone number compared to 2%. The rise of Facebook since 2006 is likely partly responsible for some of that boost.

The survey found that 60% of teens who use Facebook, the most commonly used social media site, said it was "not difficult at all" to manage the privacy controls, while less than 1% said it was "very difficult."

Among the steps they have taken to manage their privacy: 59% said they had deleted or edited something they had posted; 53% said they had deleted comments from others; 45% said they had removed their name from a photo; and almost a third (31%) had deleted or deactivated their profile or account at one time.

According to associated focus group findings conducted by the Youth and Media team at Harvard's Berkman Center for Internet & Society beginning in February, teens have mixed reaction to ad practices. Some teens were annoyed by the ads, which they called creepy when they were targeted or personalized, while others saw them as necessary or even welcomed as info on brands they liked.